Still, most people think of magnesium as a calming mineral. “It really relaxes everything in our body,” says Deepali Kashyap MD, IFMCP, NMCP, a certified functional medicine doctor with Galleria Women’s Health. “If you have leg cramps, it helps with that. If you have stomach cramps, it helps with that. It relaxes our blood vessels, so it helps to lower blood pressure.”

The best place to get your magnesium fill is through magnesium-rich foods. Though sometimes, it helps to get a boost with supplements. There are many different types of magnesium supplements—one of the most widely available and inexpensive forms being magnesium oxide.

Magnesium oxide is a salt combined with magnesium and oxygen, per the National Library of Medicine (NLM). While it’s a common form of magnesium in over-the-counter (OTC) supplements, it’s often not recommended on its own by doctors.

In other words: Magnesium oxide may not be the best type of magnesium to take if you have a deficiency, but it does have some health benefits. Learn what those are here, plus how much to get per day, and the best forms of magnesium to take for particular health issues.

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How is magnesium oxide different from other magnesium supplements?

Magnesium oxide can be found as an OTC supplement and is typically sold in tablet or capsule form. It’s frequently taken as a dietary supplement to help heartburn, sour stomach, and constipation, per the NLM.

One of the biggest differences between magnesium oxide and other magnesium supplements—such as magnesium citrate and glycinate—is that magnesium oxide has less bioavailability. That means less of the magnesium in the supplement is available for your body to use, says Brynna Connor, MD, a family medicine physician and health-care ambassador at NorthWestPharmacy.com.

In fact, a July 2019 study in Nutrients tested the bioavailability of 15 different forms of magnesium and found that magnesium oxide had the lowest solubility and, therefore, bioavailability—despite having a high amount of elemental (or total) magnesium. This means if you’re magnesium-deficient, it may not be the best form to take. (More on this below.)

What’s the best supplement to take for magnesium deficiency?

Because magnesium oxide doesn’t absorb well into the bloodstream, it doesn’t work as well as other types of magnesium that are more readily absorbed, says Dr. Connor. So if you have a deficiency, magnesium oxide won’t be as effective as other types of magnesium in raising your blood magnesium levels.

Forms of this mineral that are better absorbed than magnesium oxide—and are better for treating magnesium deficiency in general—include the following:

• Magnesium citrate
• Magnesium glycinate
• Magnesium aspartate
• Magnesium lactate
• Magnesium chloride

If you think you have a magnesium deficiency, schedule a visit with your doctor to get your blood tested. Some common signs of low magnesium levels include the following, per the U.S. National Library of Medicine:

• Loss of appetite
• Nausea
• Vomiting
• Fatigue and weakness
• Muscle cramps
• Irregular heartbeat

6 potential health benefits of magnesium oxide

Magnesium oxide is the least bioavailable of all different types of magnesium, but it does still offer some health benefits for particular issues. (Of course, if you’re dealing with any of the below, the first step is to talk to your doctor to see if a magnesium supplement is right for you.)

1. It may help relieve your headaches

Some research shows that magnesium deficiency is associated with headaches and migraines.

A February 2021 randomized controlled trial in Acta Neurologica Belgica found that 500 milligrams of magnesium oxide was effective in preventing migraine similar to the migraine medication valproate sodium. Another randomized controlled trial of 118 children found that taking 9 milligrams per kilogram of oral magnesium oxide every day significantly reduced headache days overall compared to the placebo, per a September 2020 review in Nutrients.

But magnesium oxide isn’t the only form of magnesium that’s great for migraine prevention. “The best form of magnesium for migraines or headaches is actually magnesium threonate,” says Dr. Kashyap. “We have something called a blood-brain barrier that prevents many chemicals from our body from going to our brain. And magnesium threonate is one of the forms that’s able to cross the blood-brain barrier and actually really help with headaches,” she says.

2. It may help support your body’s stress response

Magnesium plays an important role in the body’s stress response—it helps regulate the stress hormone cortisol as well as certain neurotransmitters in the brain, according to the Cleveland Clinic.

Although more research is needed, “there is some data to show that magnesium oxide can help when supplemented with vitamin B6 to reduce anxiety and stress in women, particularly those who have premenstrual syndrome,” says Dr. Connor, citing a May 2017 systematic review in Nutrients.

3. It can help relieve constipation

Plenty of research backs up magnesium oxide as a safe and effective way to find relief when you’re, ahem, backed up. “As an osmotic laxative, magnesium oxide causes your intestines to release water, which is drawn into and softens the stool, making bowel movements more frequent and stool easier to pass,” says Dr. Connor.

In fact, a January 2021 randomized, placebo-controlled trial in The American Journal of Gastroenterology found that taking 1.5 grams of magnesium oxide was just as effective as the popular laxative senna in relieving constipation. And a February 2017 randomized controlled trial in Magnesium Research found that taking 800 milligrams of magnesium oxide helped prevent constipation after cardiac surgery.

If you’re taking magnesium for gut health and constipation, it’s often in the form of a laxative—to help regulate your bowel movements.

4. It may help lower blood pressure

Magnesium helps relax our blood vessels, and as a result, may help lower blood pressure levels, says Dr. Kashyap. Though the research on this effect is limited, a small 2018 study in Nutrients found that people living with hypertension who took 300 milligrams of magnesium oxide for a month significantly lowered their blood pressure levels.

Ultimately, if you have high blood pressure, it’s best to go to your doctor to discuss certain prescription medications and lifestyle adjustments first, before trying a magnesium supplement.

5. It may help you stabilize your blood sugar

Magnesium plays a role in insulin function and breaking down carbohydrates—two factors that have an effect on blood sugar levels. This may suggest that, in some cases, taking magnesium supplements could aid your efforts to stabilize your blood sugar and insulin levels.

A May 2020 study in Lipids in Health and Disease found that taking a combination of 250 milligrams of magnesium oxide and 150 milligrams of zinc sulfate helped significant lower blood glucose levels in people with coronary heart disease (CHD) and type 2 diabetes compared to a placebo. A small March 2017 study in Medicine showed that correcting low magnesium levels by taking magnesium oxide helps improve blood sugar in children with type 1 diabetes. And another small January 2019 study in Nutrients showed that taking 250 milligrams of elemental magnesium made up of magnesium oxide, gluconate, and lactate daily for three months showed a significant improvement in HbA1C and insulin levels. However, more research is still needed to fully understand magnesium oxide’s effect on blood sugar.

Keep in mind: If you have high blood sugar levels, it’s best to first turn to lifestyle changes like watching your sugar intake, exercising, and taking prescription medications (if advised by your doctor).

6. It may help maintain your skin’s moisture and health

Because magnesium helps open up our blood vessels, it can increase the blood supply to our organs, says Dr. Kashyap. This includes your skin—aka, your body’s largest organ.

“Magnesium is necessary for maintaining skin’s moisture and minimizing water loss,” says Dr. Connor. “There is some data to show that people who have significantly dry or damaged skin also show low magnesium in their blood levels.” But keep in mind, this doesn’t mean every person with dry skin has a magnesium deficiency; more research is needed to fully understand this connection.

Potential side effects and risks of magnesium oxide

Even though it’s a natural mineral, taking magnesium supplements doesn’t come without risks. Meaning, it’s possible to take too much of it. According to Dr. Connor, signs and symptoms of taking too much magnesium (also known as magnesium toxicity) can include the following:

• Arrhythmias in the heart
• Loose stool and diarrhea
• Low blood pressure
• Facial flushing
• Urine retention
• Depression and fatigue
• Muscle weakness
• Vomiting and nausea

People who should avoid magnesium oxide

“People with chronic kidney disease should consult with a physician before taking a magnesium supplement, as an excessive amount of magnesium can accumulate in the blood if the kidneys aren’t functioning correctly,” says Dr. Connor.

It’s also important to note that certain types of magnesium supplements can have added sugar or artificial sweeteners, which may not be ideal for people with high blood sugar. Before purchasing a supplement, read the product label carefully or ask your doctor for brand recommendations.

Possible drug interactions

Magnesium oxide can also negatively interact with some drugs, including the following, per Dr. Connor:

• Levodopa/carbidopa (Sinemet)
• Certain antibiotics
• Bisphosphonates
• Calcium channel blockers
• Muscle relaxants
• Potassium-sparing diuretics
• Anticoagulant and antiplatelet drugs
• Sulfonylureas
• Antacids
• Neurontin
• Ketamine
• Sevelamer (Renagel and Renvela)

In general, it’s always a good idea to talk to your doctor before adding any supplements to your regimen to avoid any potential adverse effects.

How much magnesium oxide do you need per day?

There’s no specific daily recommendation for certain types of magnesium (i.e., magnesium oxide). But in general, adults should aim for between 310 and 420 milligrams per day (ideally from food), according to the NIH.

If you’re low or deficient in magnesium, your doctor may recommend you start a magnesium supplement. But remember, as with any other supplement, magnesium affects people in different ways and can come with varying benefits, risks, and side effects.

“I typically have patients start on any type of magnesium at 200 milligrams, and see how they do in terms of the benefits they observe, as well as the side effects,” says Dr. Connor. “I generally have them stay under 500 milligrams of magnesium per day, but because everybody is different, it’s important to discuss dosage and use with your physician.”

When to see a doctor

If you have symptoms like fatigue, nausea, weakness, loss of appetite, or muscle cramps, and you think you may be magnesium-deficient, schedule an appointment with your doctor so they can run some blood tests. If you are deficient, they’ll be able to recommend certain types of magnesium supplements to help you regain your blood magnesium levels (and it won’t likely be magnesium oxide due to its limited bioavailability).

That said, if you’re considering magnesium oxide for treating things like headaches or constipation, reach out to your doctor to see if this type of supplement is right for you.

FAQ

Should I take magnesium oxide in the morning or at night?

Dr. Kashyap recommends taking magnesium oxide earlier in the day, either with water or food. “For anything to work, it has to get absorbed. Because magnesium oxide is insoluble in water, taking it on an empty stomach means it won’t get absorbed, so it’s just going to be sitting in our stomach like a rock,” she adds.

Can you take magnesium every day?

You can take magnesium every day if you take it in small dosages (20 milligrams at a time), says Dr. Kashyap. But if you’re using magnesium oxide as a laxative in large doses (such as 1,000 milligrams), then take it for a maximum of one week, then call your doctor to find alternative methods for constipation relief.

Are there any drinks or foods high in magnesium?

Foods that are naturally high in magnesium include chia seeds, pumpkin seeds, black beans, almonds, dark chocolate, spinach, edamame, sweet potato, and avocado, per the Cleveland Clinic. There are also some drinks high in magnesium, including milk, soymilk, and hot chocolate with real unsweetened cocoa powder, per the Cleveland Clinic. And while some people think that coffee has magnesium (or that coffee depletes magnesium), there is not enough scientific evidence to support these claims.

—reviewed by Jennifer Gilbert, MD, MPH